The present invention relates to an external prosthesis for augmenting deficient anatomy, and in particular, to an external prosthesis which has both visual and tactile similarities to the natural anatomy.
Prostheses, both internal and external, are known for the purpose of augmenting deficient anatomy. Both internal and external prostheses must accurately replicate the size and shape of the deficient anatomy and if possible, the function of the replicated anatomy. External prostheses present additional unique problems in that external prostheses, since they are not implanted within the body, are more exposed to the visual and tactile impressions of the person fitted with the prosthesis, and, in some cases, to other persons as well.
An example of an internal prosthesis is Carlisle et al. (U.S. Pat. No. 5,658,330) which discloses a breast prosthesis implant with an outer elastic shell which encloses a biocompatible fluid and a silicone foam insert having the shape and consistency of breast tissue. A possible material for the outer shell is silicone. In one embodiment the foam body has a volume substantially equal to the unstretched volume of the elastic shell. The outer elastic shell may be formed on a mandrel which may also be used as the form for a mold to shape the foam insert. Among the biocompatible fluids, saline and silicone gel are disclosed. Carlisle et al. note that the prior art discloses multilumen prostheses where a lubricating material is provided between an outer shell and an inner lumen. It is also disclosed that the silicone foam body formed as described in the patent comprises both open cell and closed cell characteristics. The foam body may be either bonded to a portion of the inner surface of the shell or left free floating. The method of manufacturing the silicone foam body requires the uncured silicone to be blended with air, injected into a mold, and placed under a vacuum while the mold is heated to cure the silicone.
The outer shell of Carlisle et al. is an elastic silicone. It is disclosed that the outer shell may be formed by repeated dipping of a breast shaped mandrel in a silicone dispersion. External breast prostheses are also known having elastic hollow shells of silicone rubber molded to the shape of a breast. Examples are disclosed in Eberl et al. (U.S. Pat. No. 4,681,587), Grundei (U.S. Pat. No. 4,676,795), and Eaton (U.S. Pat. No. 5,700,288).
Internal prostheses having internal foamed bodies are known. Carlisle et al. disclose a foam body made of foamed silicone. However, polyurethane foam bodies for breast prosthesis implants are also known; e.g., Pangman (U.S. Pat. No. 3,366,975) and Ledergerber (U.S. Pat. No. 5,282,856). Greenberg (U.S. Pat. No. 5,098,330) discloses a latex foam external breast prosthesis. Eberl et al. (U.S. Pat. No. 4,681,587) disclose an external breast prosthesis member formed from silicone in the shape of a breast with a cavity on the back side. The cavity is filed with a polyurethane foam member to prevent the silicone member from collapsing. Grundei discloses an external breast prosthesis consisting of an elastic silicone shell filled partly with a plastic or rubber sponge, such as polyurethane, and partly with a slowly flowing gel-like mass.
Various filling materials are known for prostheses. Carlisle et al. disclose filing a breast prosthesis with a biocompatible fluid, such as saline or silicone gel. For the purpose of making a breast prosthesis radiolucent, the prior art teaches the use of natural triglyceride oils as filling materials in breast prostheses. In particular, Destouet et al. (U.S. Pat. No. 4,995,882) disclose biocompatible triglycerides in breast implants and suggest peanut oil and sunflower seed oil as being suitable for this purpose. Destouet et al. do not disclose using the triglyceride oil as a lubricant between the silicone shell and the foam body, but the prior art does teach the desirability of lubricants in multilumen breast implants, e.g., Shane (U.S. Pat. No. 5,358,521), and Tiffany et al. (U.S. Pat. No. 4,731,081).
Various methods are known for forming prostheses. Carlisle et al. disclose molding a foam body separately from a shell, opening the shell, inserting the foam body into the shell and resealing the shell. A similar process is disclosed in Degler et al. (U.S. Pat. No. 5,035,758) where a synthetic resin composition is cured between two thermoplastic films in a mold.
Pfrommer (U.S. Pat. No. 4,401,492) discloses a method of forming a breast prosthesis in which a mandrel shaped like a natural breast is dipped into a silicone dispersion to form the forward wall of the breast prosthesis. A rear wall is secured to the front wall and a colorant is applied to the surface. The prosthesis is then dipped into a clear silicone dispersion to form a second skin. The second skin protects the colorant on the prosthesis. A gel fill is injected into the interior space.
Ledergerber (U.S. Pat. No. 5,282,856) discloses implants which contain compressive structures designed to disorganize the formation of scar tissue.
The limitations of the prior art are overcome by the present invention as described below.
The present invention is a flexible external prosthesis which may be used to augment deficient anatomy, as for example, replacing a breast removed by mastectomy or an eye prosthesis following removal of the eye or surrounding tissue.
The prosthesis is formed by first creating a thin walled hollow shell using, e.g., the technique described in U.S. Pat. No. 5,376,323. This technique uses room temperature vulcanizable silicone to form a thin wall inside a mold adapted to reproduce precisely the shape required for anatomical augmentation. Once the thin hollow shell has been formed, the interior is filled with a flexible foam, desirably polyurethane or latex foam. The foam is formed by either of two methods. In one method the same mold used to form the thin walled hollow shell is used again to shape the foam into the identical configuration. The hollow prosthesis may then be opened and the foam body inserted and the shell resealed.
In another method, the foam is injected into the hollow shell while it is contained in the mold. The foam is desirably a two-part material which chemically generates a foaming agent when the two parts are mixed together. The foam then expands into the interior of the hollow shell and assumes the shape imposed by the mold. Multiple vents may be required to provide exit ports for the gas generated in the process.
Using either method of preparing the foam body, the foam body may not naturally attach itself to the interior surface of the silicone shell. In certain applications such as breast prostheses, however, it may be desirable that the foam body be attached to the shell at the rear wall of the shell. Movement of at least the front wall of the shell with respect to the foam body is desirable for a natural feel and appearance.
The foam body may be of either an open cell or closed cell type. To ensure free movement of the shell with respect to the foam body, the foam is lubricated, desirably using a triglyceride oil, such as soy bean oil. In the case of an open cell foam, the triglyceride oil is impregnated into the foam body. In the case of a closed cell foam, the triglyceride resides on the surface of the foam body.
By using the foam body to support the hollow prosthesis shell, it is possible to make the shell walls thinner and thus more natural in feel and appearance. It is desirable that the shell thickness be in the range of 1.0 to 2.0 mm, although in certain applications the shell thickness may be as little as 0.04 mm and may be varied over the shell for the most desirable mechanical properties.
An external prosthesis made according to this invention is intended to replicate as nearly as possible the natural feel and appearance of the anatomical feature being replicated. Accordingly, it is desirable that the foam body be colored with an opaque pigment and that the shell be colored with a translucent pigment. The combination provides a more natural replication of the appearance of human skin over underlying tissue. Additional enhancements of the natural appearance can be obtained by adding colorants to the lubricating oil; e.g., to mimic the appearance of blood below the surface of the skin. Thin hollow tubes affixed to the inner surface of the shell may mimic blood vessels and in conjunction with the appropriately colored lubricating oil provide a high degree of realistic simulation of the appearance of natural skin and the underlying tissue.
Further to enhance the natural tactile characteristics of the prosthesis, the foam body may desirably be formed at least in part with xe2x80x9caccordionedxe2x80x9d sections; i.e., sections with wedges removed so as to allow for greater resilience of portions of the foam body. The triglyceride lubrication combines with the accordioned sections to allow selected portions of the prosthesis to be compressed in a more natural manner. This technique is most likely to be applicable to external breast prostheses. In a breast prosthesis, it is desirable for a natural response that the inferior portion of the prosthesis be more compressible than the superior portion. The provision of a translucent pigment on the shell acts to hide the removed wedges of foam body and prevents the loss of the illusion of a natural appearance.
It is preferable that the prosthesis be provided with a valve for the injection of filling material. It is desirable to adjust the pressure of the filling material to achieve the optimum naturalistic resilience of the elastomer shell.
The present invention is an extremely lightweight flexible prosthesis with a thin outer shell of elastomer, such as silicone rubber, and an inner foam body, both having an elastic memory with predictable shape. The inner foam body provides resilience and support for the thin walls of the elastomeric shell. The foam body is saturated with a natural oil, such as a triglyceride oil including soybean oil, for lubrication for independent flexibility and movement between the outer shell and the inner foam body. The device provides a shape that is soft, forgiving and especially light in weight, yet maintains its original formed shape.
Since the outer shell seals the interior from contact with the atmosphere, the environment of the interior including the foam body is oxygen free. This can be important when a natural oil is used for lubrication of the foam body, since natural oils such as soybean oil oxidize and deteriorate in the presence of oxygen. Furthermore, many foamed elastomers can deteriorate when exposed to air. The inner foam body prevents the walls of the outer shell from collapse, rippling, crimping and creasing. Also the support provided by the inner foam body allows the walls of the shell to be made thinner for more flexibility and natural feel. Thin elastomer walls are also subject to tearing which is alleviated by the support provided by the foam body.
A prosthetic device made according to the present invention may be employed for alloplastic restoration, reconstruction of ablative facial, head and neck disease or trauma, mastectomies, and amputations. The device is however preferably limited to external prosthetic applications and is not implantable.
It is therefore an object of the present invention to provide for an external prosthesis which has properties that provide both visual and tactile similarities to natural human anatomy.
This and other objects and advantages of the present invention will be apparent from a consideration of the following detailed description of the preferred embodiments in conjunction with the appended drawings as described following.